During the last seven years, there have been major advances in our understanding of normal cellular events that lead to activation of the c- Src protein tyrosine kinase and the structure and function of individual domains of Src. The experiments in this proposal address several important issues relating to the specific role of the Src protein in receptor signaling pathways, the mechanisms involved in Src activation and the specific functions of the two binding domains of Src, the Src homology 2 (SH2) and Src homology 3 (SH3) domains. A major focus of the proposal will be on the involvement of Src in pathways regulated by integrin family receptors which mediate the adhesion of cells to the extracellular matrix and activate intracellular events that regulate cell morphology, migration, differentiation, and proliferation. This study will examine the role of Src in the organization of focal adhesion complexes, phosphorylation of focal adhesion proteins, and activation of downstream signaling pathways regulated by integrins. In addition, the experiments will examine the role of the Src SH2 and SH3 domains in integrin-regulated events. A second aim of the proposal is to examine the role of Src autophosphorylation in controlling the catalytic activity of Src as well as in the activation of cellular events regulated by Src (adhesion, mitosis, growth factor stimulation, and stress responses). The experiments involve the (1) identification of normal cellular events that lead to phosphorylation of the Src autophosphorylation site Y416, (2) elucidation of the mechanism of phosphorylation at Y416, (3) analysis of the role of Y416 phosphorylation for Src-mediated events, and (4) examination of the importance of phosphorylated Y416 in Src association with cellular binding proteins. Lastly, the experiments specifically focus on the properties of SH3 domains that affect the specific interaction of Src with cellular substrates. Given the role of Src and related kinases in cellular events that affect cellular proliferation (growth factor stimulation and mitosis), cellular adhesion, and stress induced angiogenesis, the studies in the proposal should help elucidate the basic cellular mechanisms involved in these processes and contribute to a better understanding of the mechanisms leading to oncogenic transformation by mutant forms of the Src protein.